The display of rendered images, for example 3D or 2D images, by processing and rendering volumetric image data obtained using any of a variety of different imaging modalities is increasingly common. Such imaging modalities include, but are not limited to ultrasound imaging, MRI, CT, PET and the like.
It is often desired to view only certain features of interest, for example vessels, bone, flesh, or selected anatomical features. There are numerous known automatic segmentation algorithms that can be used to extract and render only image data relating to such features of interest, for instance to extract and render only bone, or vessels. Such vessels can include, for example, vessels forming part of the vasculature system, the lymph system, the nervous system, or airways.
Some such known automatic segmentation algorithms generate masks that can be used to mask out data that does not relate to the current region of interest, for example to mask out data representing regions of bone, or regions where a gantry table or other equipment, or other artefact, is present.
It can be difficult for known automatic segmentation algorithms to distinguish accurately between substances of different types in some circumstances.
For example, when viewing CT angiography data in SVR, vessels are commonly obstructed by bone. Automatic bone segmentation algorithms are commonly used to identify the bone and remove it from visualization. However, it is difficult to distinguish vessel, when injected with a contrast agent, and bone in CTA data (they have very similar intensity), and automatic bone segmentation occasionally incorrectly identifies some vessel as bone. Such incorrect identification of vessels as bone can lead to occlusion of vessels, such that when the identified bone data is subtracted and the remaining vessel data is rendered, some parts of the vessel can seem to be missing.
There is significant anatomical variation in bone and vessel size throughout the body, and misidentification of bone as vessel, or vice versa, can commonly occur when a contrasted vessel or vessels are in close proximity to bone. The most common anatomical regions where this occurs is the branch of the iliac artery passing just under the pelvis, the aorta near the spine, and femoral and other arteries in the legs near the femur and other long bones. Errors commonly misidentify small (approximately 1 to 2 cm) sections of vessel as bone, particularly where there is little intensity variation between vessel and bone. These sections appear to the user as gaps in the contrasted vessels in the SVR view.
It is known to enable a user to manually adjust regions, for example to manually identify regions as being vessel rather than bone. However, that can be time-consuming and inefficient for the user, for example a radiographer or radiologist.
There have been attempts to increase the sophistication of automatic segmentation algorithms to reduce misidentification of vessel and bone.